This invention was not made by an agency of the U.S. Government or under a contract with any agency of the U.S. Government.
Not applicable.
Not applicable.
The present invention relates generally to belt drives and more particularly to a method and apparatus for protection from damage following failure of, for example, a toothed belt drive as utilized for example in timing belt applications. Timing belt failure may result in expensive damage and/or dangerous consequences, so that the detection of incipient belt failure in this application is very useful and important.
Toothed belt drives are commonly utilized for mechanical power transmission, particularly where a correct angular relationship or xe2x80x9ctimingxe2x80x9d between a driving shaft and a driven shaft needs to be accurately maintained.
Vehicles utilizing internal combustion engines typically have a camshaft with spaced cams mounted on the camshaft for opening and closing engine valves in accordance with the requirements of the engine operating cycle. Some engines use a single camshaft whereas others utilize a plurality of camshafts, for example, two camshafts. The camshafts are typically driven by the engine crankshaft which also transmits the engine power through the vehicle transmission to the wheels.
A typical application for a toothed belt drive is, for example, in a four-stroke cycle automotive engine wherein a camshaft used for operating valves runs at one-half the angular velocity or, otherwise expressed, at one-half the revolutions per minute (rpm) of the crankshaft that drives it by way of the toothed belt and wherein the angular position relationship or timing of the camshaft and crankshaft needs to be maintained accurately.
Traditionally in the past, xe2x80x9clink chainsxe2x80x9d or bicycle chain type timing chains, sometimes utilizing double side by side chains, have been used in car engines to couple the crankshaft to the camshaft, using a driven camshaft sprocket having twice as many teeth as a driving crankshaft sprocket. In some engines, a timing gear train has been used to drive the camshaft from the crankshaft.
Chains and gears are both capable of driving a camshaft while maintaining the required timing relationship between the camshaft and the crankshaft. However, the high cost of chain and gear drives and, to some extent, their operating noise level have more recently led to the widespread use of toothed belts for coupling the crankshaft and the camshaft in automotive engines, particularly in smaller engines. A toothed belt drive is quiet and well suited to driving the camshaft while maintaining the required timing relationship to the crankshaft. The same timing belt drive may also be used to drive, for example, a fuel injection pump, an ignition distributor, or some other accessory.
Examples of toothed belt and timing chain drives may be found in, for example, U.S. Pat. No. 5,463,898 entitled METHOD OF DETECTING TIMING APPARATUS MALFUNCTION IN AN ENGINE issued Nov. 7, 1995 in the name of Blander et al.; and U.S. Pat. No. 5,689,067 entitled DIAGNOSTIC METHOD AND APPARATUS FOR MONITORING THE WEAR OF AT LEAST AN ENGINE TIMING CHAIN issued Nov. 18, 1997 in the name of Klein et al., whereof the disclosure is herein incorporated by reference to the extent it is not incompatible with the present invention.
While a toothed timing belt drive offers advantages, the likelihood of belt failure is present. If a timing belt breaks in such an engine, the camshaft will very soon stop rotating, while the crankshaft will typically continue to turn for a time, either due to its rotational momentum and/or because it is coupled to the driving wheels which continue to turn because of the vehicle""s momentum.
In some cases, repairing the engine following such a timing belt failure may merely require realigning the camshaft and the crankshaft into proper relationship and replacing the belt. Naturally, the vehicle will be inoperable until the belt is replaced, generally in a repair shop, and the operator may be stranded. Furthermore, since a broken timing belt can cause instant and total loss of power at an unexpected moment, a potentially hazardous traffic situation can result.
Furthermore, in a number of engines, such as those utilizing a high compression ratio, clearance space at the top of the cylinders may be very restricted such that the pistons can only move freely to the top of their stroke with valves in the closed position.
In such an engine, if the crankshaft is rotating and the camshaft stops so that a valve is held open by its cam, interference between a piston and a stopped valve can occur so that a piston can collide with the stopped valve. This generally leads to extensive damage, and possibly ruining the engine so that the cost of repair is no longer economically justifiable. The likelihood that the problem of valve/piston interference will occur in at least one cylinder of such an engine is generally very high upon loss of a timing belt.
When such interference occurs after timing belt breakage, damage may range from a bent valve, and/or a hole in a piston, damage to a cylinder head and/or a camshaft, a gouged cylinder head, to a completely ruined engine. Furthermore, if the car is being driven at the time of the belt failure, the engine may become locked by the collision of a piston with a valve so that the driving wheels may also become locked, thereby possibly creating a hazardous situation in traffic.
As was stated above, the problem of serious damage following timing belt failure is very likely to occur in high compression ratio engines. These include many high-performance engines and compression-ignition or xe2x80x9cdieselxe2x80x9d engines wherein the very high compression ratio needed for ignition generally leaves insufficient room for a piston to avoid hitting a valve held open by an inoperative camshaft. Despite the problems consequent on timing belt failure, car manufacturers continue to build such xe2x80x9cinterference enginesxe2x80x9d which exhibit the problem, apparently because a xe2x80x9cfree-running enginexe2x80x9d with enough clearance results in lower performance. The problem represents a weak point in engine reliability and, given the usually catastrophic damage resulting from timing belt failure, is likely to result in lowering of customer confidence in the product. Utility type vehicles and other vehicles intended to provide dependable performance in remote areas are thereby made less reliable in a rather unpredictable manner.
The problem of serious damage caused by timing belt failure in automotive engines has been addressed to some extent by maintenance schedules for periodically replacing toothed timing belts in such engines at an interval based on the average life expectancy of such belts. For example, an extensive list of xe2x80x9cinterference enginesxe2x80x9d, that is, engines where serious damage is likely following timing belt failure, was made available by The Gates Rubber Company on the Internet at the address http://www.gates.com/interfer.html. Manufacturer""s service manuals generally suggest periodic replacement of the belt as precautionary maintenance every 60,000 to 80,000 miles of driving or so.
One manufacturer is understood to provide a belt replacement warning light which indicates when a prescribed odometer mileage has been reached at which point presumably the belt has become less reliable. Nonetheless, failure may occur at any time before the prescribed mileage has been reached.
However, even periodic scheduled belt replacement can, at best, only reduce the average probability of belt failure: an individual belt may exhibit a shorter operating life than the average and, even with a new belt installed, initial failure remains a possibility, resulting in expensive damage to an engine. Generally, the timing belt in a typical automotive engine is not readily visible to the operator and regular inspection to ascertain the condition of a timing belt is inconvenient, even if it were a reliable way of predicting failure.
Typically, timing belt replacement as a maintenance service requires to be performed by qualified personnel in a repair shop and so is typically not an inexpensive job. In practice, it may not always be performed at the recommended intervals.
Reference is made to applicant""s application Ser. No. 09/067,390, entitled METHOD AND APPARATUS FOR TIMING BELT DRIVE, filed Apr. 28, 1998, issued Jan. 30, 2001 as U.S. Pat. No. 6,181,239, whereof the disclosure is hereby incorporated herein by reference to the extent it is not incompatible with the present invention, and which discloses a timing belt system for an engine which includes a first timing belt coupling the camshaft to the crankshaft; a second timing belt coupling the camshaft to the crankshaft; a belt sensor coupled to at least one of the first and second timing belts; and an alarm coupled to the belt sensor. In accordance with an aspect of the afore-mentioned U.S. Pat. No. 6,181,239, a method for driving a camshaft from a crankshaft of an automotive engine comprises: operating first and second toothed belts in parallel so that the engine exhibits a first mode of operation wherein both the first and second timing belts are operating, and a second mode of operation wherein one of the first and second timing belts is broken and only one of the first and second belts is operating; detecting when engine operation changes from the first mode of operation to the second mode of operation; and thereupon alerting the operator, such as by operating an alarm.
The question of timing belt failure and maintenance is extensively reviewed in the references cited in the aforementioned U.S. Pat. No. 6,181,239 to which attention is hereby directed.
The problem of belt failure has been addressed in, for example, U.S. Pat. No. 4,488,363 entitled COMBINATION IDLER AND BELT FAILURE SWITCH FOR A DRYER issued Dec. 18, 1984 in the name of Jackson et al., whereof the disclosure is herein incorporated by reference to the extent it is not incompatible with the present invention. In this patent, an arrangement is disclosed for terminating the operation of a dryer upon breakage of the drive belt. It is herein recognized that such an approach will not be useful in avoiding damage due to timing belt failure in an automotive engine, since failure of the timing belt may cause damage to follow immediately upon belt failure and the engine typically cannot practicably be stopped before the damage has taken place.
U.S. Pat. No. 4,626,230 entitled DEVICE FOR SENSING DAMAGE TO A COGGED BELT issued Dec. 2, 1986 in the name of Yasuhara discloses a device that senses deformation of the belt resulting from damage to at least one of the teeth on the belt. The device senses an opening between the belt and the pulley which results from breakage of at least one of the teeth on the belt. When such displacement or an opening is detected, an indicator lamp is lit to report that the belt should be replaced. However, if the belt itself breaks as a result of a damaged tooth, engine damage may still occur.
U.S. Pat. No. 5,994,712 entitled BELT FLAW DETECTOR issued Nov. 30, 1999 and filed Jul. 29, 1997 in the name of Mack discloses a belt flaw detector that has a light source, a sensor, and processing and signaling means to indicate and warn of the flaw in the belt.
An English-language version of Patent Abstracts of Japan, Publication Number 0906069A entitled MONITOR FOR CUTTING OF TIMING BELT OF ENGINE published 04.03.97 in the name of Takahiro discloses an xe2x80x9cextremely small conductorxe2x80x9d buried under the surface of a timing belt which is disposed between the camshaft and crankshaft of an engine, and which is put into contact with two contacts for supplying a current while the shafts are rotated. A contact setting device is supplied with power from the battery of an automobile and a very small current is passed through one contact, the conductor and the other contact. When the belt is cut, the conductor is cut and the current is cut and under this condition, a signal operates a warning device to warn a driver that the belt is cut, thereby preventing xe2x80x9ca secondary disasterxe2x80x9d or accident.
As understood from an English-language translation, Japanese patent document No. 9-60694, entitled in a translation xe2x80x9cA DEVICE FOR MONITORING ANY CUTOFF OF A TIMING BELT IN AN ENGINExe2x80x9d discloses a conductive wire embedded along with the outer surface of the timing belt. A minute current flows from one contact of a roller form and which rotates in contact with the outer surface of the timing belt, to the conductive wire and further flows to another contact to a controller. In accordance with the translation, if the conductive wire is cut, the controller fails to detect the specified current and an alarm is operated. Other arrangements are also described for monitoring rotation time and ductility of the belt.
Korean patent document No. 169630 with the translated title xe2x80x9cAN EARLY SENSING DEVICE FOR SENSING ANY DAMAGE OF A TIMING BELT EARLY IN AN INTERNAL COMBUSTION ENGINExe2x80x9d discloses, in an English language translation, a coil made of a conductor, which is embedded in the inside of the timing belt along with the gear teeth configuration and a steel wire connected with the coil, which is installed in the outer face of the timing belt so that the steel wire may be exposed to the outside of the timing belt. The disclosed arrangement also consists of a sensor supported by a separate supporter, which is installed in contact with the steel wire, an electronic controller through which the sensor is connected with and alarm, and alarm to give an alarm signal depending upon the signal sensed by the sensor.
According to the translation of Korean patent document No. 169630, in case a gear tooth of the timing belt is lost, the coil embedded in the inside of the timing belt along with the gear tooth configuration gets to be cut off If a tooth formed in the timing belt is cut off, the coil embedded in the gear tooth xe2x80x9calso gets to be short-circuited (sic)xe2x80x9d (so stated in the translation) and therefore the electrical resistance of the coil and the steel wire xe2x80x9cgets to be increased infinitelyxe2x80x9d and the sensor in contact with the steel wire senses the increased electrical resistance and generates a corresponding signal.
Korean patent document No. 169630 also states, in translation, that the steel wire is exposed to the outside of the timing belt so that it may be in direct contact with the sensor or the outer face of the timing belt can be coated with any coating agent having conductivity so that such coating agent may be electrically connected with the coil embedded in the inside of the timing belt and further the sensor may be in contact with the conductive coating agent.
Korean patent document No. 169630 states that the sensor can be of various types. The document discloses a sensor of the contact type and this is stated to be the most preferable sensor for sensing the electrical resistance of the coil and the steel wire. It is further stated in translation in Korean patent document No. 169630 that the sensor can be of the non-contact type so that xe2x80x9csuch cutoff may be directly and immediately sensed by the sensor.xe2x80x9d However, it is noted that Korean patent document No. 169630 states that such non-contact type xe2x80x9cis not preferable because it requires a complicated installation and operation as well as a high cost.xe2x80x9d.
The disclosure of the foregoing documents is hereby incorporated by reference to the extent that it is not incompatible with the present invention.
Both Japanese patent document No. 9-60694 and Korean patent document No. 169630 monitor electrically the condition of a wire embedded in a timing belt through mechanical touching of the wire by electrical contacts. Upon undue stretching or deformation of the timing belt, the condition of the wire is altered. The embedded wire can be arranged to break upon the fracture of a belt tooth or undue extension of the belt, either of which conditions can be a precursor of an imminent break in the belt. An early warning can therefore be given of an expected break in a relatively short time, if such systems were to operate reliably.
However, both Japanese patent document No. 9-60694 and Korean patent document No. 169630 use electrical contacts touching rapidly moving wires, so that the contact either slides or rolls on the wire for passing a monitoring current through the imbedded wire for signaling a change in its electrical resistance. It is herein recognized that such sliding or rolling contacts running against a small, fast-moving conductor are notoriously difficult to maintain reliably. Unreliable sliding contacts, particularly for small currents, are known from many everyday examples. A common well-known example is the operation of typical low-voltage electric toy trains, where specks of dirt, rail oxidation, and contact pressure variations tend to interfere frequently with the operation. Sliding contacts against a fine wire embedded in a moving belt are also likely to be highly problematic in practice, particularly in the environment under the engine hood of an automobile vehicle. Fast sliding at high RPM, prolonged use, prolonged non-use, movement, wear, vibration, irregularity in the belt, and dirt and oxidation deposits are likely to render the contact erratic, thereby making the system unreliable and subject to wear. For a system using contacts, the wire is, at least in part, exposed to the outside rather than being completely imbedded in the belt. Contact wear may necessitate frequent and regular contact replacement at an expense comparable to opening the timing belt compartment for belt examination or replacement and is therefore more likely to be neglected. Furthermore, such unreliable operation is particularly undesirable in a warning system for indicating timing belt damage. Typically, an erratic or unreliable warning light or sound will annoy the user and will eventually tend to be ignored, thereby defeating the purpose.
In accordance with an aspect of the invention, apparatus for monitoring a change of condition in a drive belt comprises a first inductance coil; a second inductance coil; an electrically conductive loop associated with the drive belt for motion therewith, the conductive loop forming a mutual inductive link coupling between the first and second inductance coils; and a detector coupled to at least one of the first and second inductance coils for indicating a change in the mutual inductive link coupling.
In accordance with another aspect of the invention, the apparatus comprises a first inductance coil; a source of an alternating current coupled to the first inductance coil; a second inductance coil; an electrically conductive loop coupled for movement with the drive belt, the conductive loop forming a mutual inductive link coupling between the first and second inductance coils for inducing an electromotive force in the second inductance coil; and a detector coupled to the second coil for monitoring a change in the electromotive force in the second coil.
In accordance with another aspect of the invention, a method for monitoring a change of condition in a drive belt comprises the steps of associating an electrically conductive loop for movement with the drive belt; mutually inductively coupling a first inductance coil and the conductive loop; mutually inductively coupling a second inductance coil and the conductive loop, such that the conductive loop forms a link coupling between the first and second inductance coils; passing an alternating current through a first inductance coil; and detecting a change in electromotive force in the second coil.
In accordance with an aspect of the invention, apparatus for monitoring a change of condition in a drive belt comprises a first inductance coil; a second inductance coil; an electrically conductive loop associated with the drive belt for motion therewith, the conductive loop forming a mutual inductive link coupling between the first and second inductance coils; and a detector coupled to at least one of the first and second inductance coils for indicating a change in the mutual inductive link coupling.
In accordance with another aspect of the invention, the detector monitors induced voltage or electromotive force in one of the first and second coils.
In accordance with another aspect of the invention, the conductive loop comprises a conducting wire embedded at least in part in the belt.
In accordance with another aspect of the invention, direct mutual inductive coupling between the first and second coils is small as compared with the mutual inductive coupling provided by the mutual inductive coupling provided by the link coupling.
In accordance with another aspect of the invention, apparatus for monitoring a change of condition in a drive belt comprises a first inductance coil; a source of an alternating current coupled to the first inductance coil; a second inductance coil; an electrically conductive loop coupled for movement with the drive belt, the conductive loop forming a mutual inductive link coupling between the first and second inductance coils for inducing an electromotive force in the second inductance coil; and a detector coupled to the second coil for monitoring a change in the electromotive force in the second coil.
In accordance with another aspect of the invention, the belt is a toothed timing belt and wherein the electrically conductive loop follows a path in the belt in proximity to its teeth for providing an impedance change indication of tooth damage.
In accordance with another aspect of the invention, a method for monitoring a change of condition in a drive belt comprises the steps of: associating an electrically conductive loop for movement with the drive belt; mutually inductively coupling a first inductance coil and the conductive loop; mutually inductively coupling a second inductance coil and the conductive loop, such that the conductive loop forms a link coupling between the first and second inductance coils; passing an alternating current through a first inductance coil; and detecting a change in electromotive force in the second coil.